The present invention relates to a ventricular assist device (VAD), and more particularly to a VAD which is essentially implantable in a patient.
VAD's and LVAD's, and especially VAD's and LVAD's which are more or less implantable within the body of a patient, are well known in the art. The LVAD was developed for the treatment of end stage congestive heart failure (CHF) in patients who are on maximal medical therapy and require long-term mechanical circulatory support, for example, patients who are not (temporarily or permanently) candidates for heart transplantation. Accordingly, the LVAD replaces or augments the function of the left ventricle in patients whose native left ventricles are unable to supply sufficient cardiac output to support a reasonable lifestyle, but whose right ventricle does function acceptably. The primary purpose of the LVAD, therefore, is to provide systemic blood flow equal to that provided to it by the right heart. Secondarily, it should do so in a manner that drains the pulmonary veins and left atrium effectively, thereby avoiding pulmonary complications that would affect pulmonary or right heart function.
Alternatively a VAD could be applied to replace or augment the function of the right ventricle. For the purposes of the present invention the VAD design applies to both LVAD's and RVAD's.
The implantable subsystems of the LVAD include: inlet and outlet cannulae, blood pump, controller, internal coil, compliance chamber, and infusion port subsystems. The external or non-implantable subsystems of the LVAD include: power transmitter (PT) with external coil, power pack, and battery charger. The implantable and external subsystems work together to supplement the depressed cardiac-output state of a patient whose heart is failing.
However, the known more-or-less implantable LVAD's have not proved to be entirely satisfactory in use for a variety of different reasons as follows:
First, the gas passing between the blood pump and the compliance chamber typically carries with it entrained or dissolved liquid, such as moisture. This entrained or dissolved liquid separates from the gas within the compliance chamber due to the temperature differential between the substantially spaced apart pump and compliance chamber, and under the influence of gravity accumulates at the bottom of the compliance chamber. The collected liquid at the bottom of the compliance chamber consumes its volumetric space and reduces the functionality of the chamber, thereby decreasing the efficiency of the pump. PA1 Second, the outlet cannula is connected to the blood pump at one end and to the aorta at the other end. If the outlet cannula is formed exclusively of polymer tubing, the anastomotic connection between the tube and the patient's aorta would be difficult. If the outlet cannula is formed exclusively of hard polymer tubing, then the outlet cannula is too rigid and lacks the flexibility to accommodate various movements of the patient during use. Accordingly, it is common practice to have an outlet cannula which comprises a hard polymer tubing commencing adjacent the pump and a relatively soft woven graft tubing (e.g., made of woven dacron, PTFE, etc.) adjacent to the aorta. Clearly, the securing together of the distal end of the hard polymer tubing and the proximal end of the graft tubing must provide a smooth transition and be easy to effect in manufacturing. PA1 Third, an inlet cannula is connected to the blood pump at a proximal end and to a titanium tube entering a heart chamber (e.g., the left ventricle) at a distal end. Preferably the distal end of the inlet cannula includes a sewable flexible apical cuff to facilitate attachment of the cannula to the heart chamber (e.g., the left ventricle) myocardium via surgical sewing. The means conventionally used for securing together the apical cuff and the titanium tube are complex and unreliable. The securing means must be easily utilized during the surgical implantation procedure and establish a reliable connection thereafter as a failure of the connection would be critical.
Accordingly, it is an object of the present invention to provide an improved VAD and, more particular, an improved implantable VAD.
Another object is to provide a VAD enabling accumulated liquid within the compliance chamber to be withdrawn through a subcutaneous port.
A further object is to provide a VAD including means for easily and reliably securing together in the outlet cannula the hard polymer tubing and the woven graft tubing.
It is an object of the present invention to provide a VAD including an easy-to-operate and reliable means for securing together the apical cuff and the tube entering the heart chamber (e.g., the left ventricle).
It is also an object to provide a VAD which has means for draining accumulated liquid from the compliance chamber through a subcutaneous port, an inlet cannula having components which are easily and reliably secured together without relative rotation thereof, and means for easily and reliably securing together a tube entering the heart chamber (e.g., the left ventricle) and a sewable flexible apical cuff.
It is another object to provide such a VAD which is simple and economical to assemble, implant and maintain.